Question

On passing vapours of an organic liquid over finely divided Cu at 573K the product was an alkene. This reaction is
A. Catalytic oxidation of primary alcohol
B. Catalytic dehydrogenation of secondary alcohol
C. Catalytic dehydrogenation of tertiary alcohol
D. Catalytic dehydration of tertiary alcohol

Answer 1

Hint: In this question we have to check the options and find out which one of them produces an alkene at the end after passing vapours of an organic liquid over finely divided Cu at 573K. We have to check the mechanisms of catalytic oxidation of primary alcohol, catalytic dehydrogenation of secondary alcohol, catalytic dehydrogenation of tertiary alcohol and catalytic dehydration of tertiary alcohol.

Complete Step by Step Answer:
When an alcohol's vapours are passed over a copper catalyst that has been heated to 573 K. It goes via dehydrogenation (loss of hydrogen or oxidation). This reaction is also used to differentiate between the three groups of alcohols because the product generated depends on the alcohol. When tertiary alcohol reacts with a copper catalyst at 573 K, it does not undergo dehydrogenation, instead producing the matching alkene.

Therefore, the reaction is catalytic dehydration of tertiary alcohol to an alkene.

The correct answer is D.

Additional Information: Depending on the conditions of the reaction, primary alcohols can be converted to either aldehydes or carboxylic acids. When carboxylic acids are created, the alcohol is first converted to an aldehyde and then further converted to the acid. Secondary alcohols yield ketone and tertiary alcohols yield alkene during catalytic dehydrogenation. Both primary and secondary alcohols exhibit beta-elimination, in which the alcoholic group contains both alpha and beta carbon hydrogen.

Note: Dehydrogenation of primary and secondary alcohols results in the formation of aldehyde and ketone, respectively, when their vapours are passed over heated copper at 573 K, while dehydration of tertiary alcohols results in the formation of an alkene.